1. Field of the Invention
The present invention relates to an improvement in an electrostatic chucking system having an electrode for chucking a semiconductor substrate or wafer. More particularly, the present invention relates to an improvement in an electrostatic chuck for holding a wafer during processing of a wafer, such as formation of a film, which involves a change in the temperature of the wafer.
2. Background Art
In a semiconductor manufacturing process, an electrostatic chuck has conventionally been used for fixing and holding a semiconductor substrate at the time of processing of a semiconductor substrate (i.e., a semiconductor wafer) by means of a sputtering apparatus or a dry etching apparatus. In this case, a wafer is fixed by means of a voltage applied to an electrostatic chuck. FIG. 4 is a graph showing application of a voltage to the electrode of a conventional electrostatic chuck, in which a predetermined voltage is applied to the electrostatic chuck at a required point in time.
In a process, such as a hot aluminum (Hot Al) process or a reflow aluminum (Reflow Al) process, in which a film is formed while involving a change in the temperature of the wafer, the wafer tends to warp or bend. The amount of warpage arising in the wafer or expansion of the wafer varies with a change in the temperature of the wafer in a film formation process. For this reason, the wafer cannot be properly chucked or held by use of an electrostatic chuck. Alternatively, there arises a failure, such as a wafer held by an electrostatic chuck coming off the electrostatic chuck during the film formation process. There also arise problems, such as an increase in the amount of contaminants included in the underside of a wafer or occurrence of cracks in a wafer.
The present invention has been conceived to solve such a problems in the background art and is aimed at providing an electrostatic chucking system capable of stably holding a wafer.
According to one aspect of the present invention, an electrostatic chucking system comprises an electrostatic chuck, a power supply and a voltage control section. The electrostatic chuck has an electrode for chucking a semiconductor substrate. The power supply section applies a voltage to the electrode. The voltage control section controls the applied voltage, wherein the voltage control section varies and controls the applied voltage stepwise.
In another aspect, in the electrostatic chucking system, a temperature sensor may be provided for detecting the temperature of the semiconductor substrate held by the electrostatic chuck, wherein a signal output from the temperature sensor is input to the voltage control section to thereby control the applied voltage.
In another aspect, in the electrostatic chucking system, a warpage sensor may be provided for detecting the amount of warpage arising in the semiconductor substrate held by the electrostatic chuck, wherein a signal output from the warpage sensor is input to the voltage control section to thereby control the applied voltage.
In another aspect, in the electrostatic chucking system, a distance sensor may be provided for detecting the distance between the electrostatic chuck and the semiconductor substrate held by the electrostatic chuck, wherein a signal output from the distance sensor is input to the voltage control section to thereby control the applied voltage.
Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings.